Portugal only has one tournament per season, it's a much bigger tennis country than Canada and only invites one Portuguese per year, even though it's a clay MM tournament!
Giving a WC to some Canadian who won't win more than six games in his match instead of giving it to Ferrero is pure ridiculous!
Just because a tournament in Portugal gives only one home WC is no reason for the Rogers Cup to do it. Giving even one WC to a foreign player hasn't been common over the last several years, two would be extremely unlikely, unless it was someone on the same level of interest from casual fans as Safin/Hewitt.
Personally, I'd be pretty ticked off if Tennis Canada gave the fourth WC to a guy like Ferrero instead of to a Canadian, even though the Canadian would have much weaker odds of winning a match. The tournament is run by Canadian tennis, and paid for by the interest and attendance of Canadian fans and sponsors. So it makes perfect sense to me that the WC's should benefit Canadian tennis as well
If it's Bruno, it's a chance to give a (hopefully) rising star some well-needed experience. If it's Fred, it'll be a an opportunity to give a guy who was the #1 Canadian for a fair period of time, and a Davis Cup stalwart for a decade, a proper send-off at a big event. Either seems to me a much more compelling story from a Canadian perspective than Ferrero playing would be.
From an international perspective, you're right, fans from other countries probably would find one (or even zero) Canadians better. But that's not what WCs are for, in my mind.
Sigh, I didn't mean to rant quite so much about that